//
// Created by Jisam on 2024/5/28.
//
#include "bits/stdc++.h"

using namespace std;
int prime[168] = {2, 3,
                  5, 7, 11, 13, 17, 19, 23, 29, 31, 37,
                  41, 43, 47, 53, 59, 61, 67, 71, 73, 79,
                  83, 89, 97, 101, 103, 107, 109, 113, 127, 131,
                  137, 139, 149, 151, 157, 163, 167, 173, 179, 181,
                  191, 193, 197, 199, 211, 223, 227, 229, 233, 239,
                  241, 251, 257, 263, 269, 271, 277, 281, 283, 293,
                  307, 311, 313, 317, 331, 337, 347, 349, 353, 359,
                  367, 373, 379, 383, 389, 397, 401, 409, 419, 421,
                  431, 433, 439, 443, 449, 457, 461, 463, 467, 479,
                  487, 491, 499, 503, 509, 521, 523, 541, 547, 557,
                  563, 569, 571, 577, 587, 593, 599, 601, 607, 613,
                  617, 619, 631, 641, 643, 647, 653, 659, 661, 673,
                  677, 683, 691, 701, 709, 719, 727, 733, 739, 743,
                  751, 757, 761, 769, 773, 787, 797, 809, 811, 821,
                  823, 827, 829, 839, 853, 857, 859, 863, 877, 881,
                  883, 887, 907, 911, 919, 929, 937, 941, 947, 953,
                  967, 971, 977, 983, 991, 997,};
bool isprime[1010] = {0, 0, 1, 1, 0, 1, 0, 1, 0,
                      0, 0, 1, 0, 1, 0, 0, 0, 1, 0,
                      1, 0, 0, 0, 1, 0, 0, 0, 0, 0,
                      1, 0, 1, 0, 0, 0, 0, 0, 1, 0,
                      0, 0, 1, 0, 1, 0, 0, 0, 1, 0,
                      0, 0, 0, 0, 1, 0, 0, 0, 0, 0,
                      1, 0, 1, 0, 0, 0, 0, 0, 1, 0,
                      0, 0, 1, 0, 1, 0, 0, 0, 0, 0,
                      1, 0, 0, 0, 1, 0, 0, 0, 0, 0,
                      1, 0, 0, 0, 0, 0, 0, 0, 1, 0,
                      0, 0, 1, 0, 1, 0, 0, 0, 1, 0,
                      1, 0, 0, 0, 1, 0, 0, 0, 0, 0,
                      0, 0, 0, 0, 0, 0, 0, 0, 1, 0,
                      0, 0, 1, 0, 0, 0, 0, 0, 1, 0,
                      1, 0, 0, 0, 0, 0, 0, 0, 0, 0,
                      1, 0, 1, 0, 0, 0, 0, 0, 1, 0,
                      0, 0, 0, 0, 1, 0, 0, 0, 1, 0,
                      0, 0, 0, 0, 1, 0, 0, 0, 0, 0,
                      1, 0, 1, 0, 0, 0, 0, 0, 0, 0,
                      0, 0, 1, 0, 1, 0, 0, 0, 1, 0,
                      1, 0, 0, 0, 0, 0, 0, 0, 0, 0,
                      0, 0, 1, 0, 0, 0, 0, 0, 0, 0,
                      0, 0, 0, 0, 1, 0, 0, 0, 1, 0,
                      1, 0, 0, 0, 1, 0, 0, 0, 0, 0,
                      1, 0, 1, 0, 0, 0, 0, 0, 0, 0,
                      0, 0, 1, 0, 0, 0, 0, 0, 1, 0,
                      0, 0, 0, 0, 1, 0, 0, 0, 0, 0,
                      1, 0, 1, 0, 0, 0, 0, 0, 1, 0,
                      0, 0, 1, 0, 1, 0, 0, 0, 0, 0,
                      0, 0, 0, 0, 1, 0, 0, 0, 0, 0,
                      0, 0, 0, 0, 0, 0, 0, 0, 1, 0,
                      0, 0, 1, 0, 1, 0, 0, 0, 1, 0,
                      0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
                      0, 0, 1, 0, 0, 0, 0, 0, 1, 0,
                      0, 0, 0, 0, 0, 0, 0, 0, 1, 0,
                      1, 0, 0, 0, 1, 0, 0, 0, 0, 0,
                      1, 0, 0, 0, 0, 0, 0, 0, 1, 0,
                      0, 0, 0, 0, 1, 0, 0, 0, 0, 0,
                      1, 0, 0, 0, 1, 0, 0, 0, 0, 0,
                      1, 0, 0, 0, 0, 0, 0, 0, 1, 0,
                      0, 0, 1, 0, 0, 0, 0, 0, 0, 0,
                      1, 0, 0, 0, 0, 0, 0, 0, 0, 0,
                      1, 0, 1, 0, 0, 0, 0, 0, 0, 0,
                      0, 0, 1, 0, 1, 0, 0, 0, 0, 0,
                      1, 0, 0, 0, 1, 0, 0, 0, 0, 0,
                      1, 0, 0, 0, 0, 0, 0, 0, 1, 0,
                      0, 0, 1, 0, 1, 0, 0, 0, 1, 0,
                      0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
                      1, 0, 0, 0, 0, 0, 0, 0, 1, 0,
                      0, 0, 1, 0, 0, 0, 0, 0, 0, 0,
                      1, 0, 0, 0, 1, 0, 0, 0, 0, 0,
                      1, 0, 0, 0, 0, 0, 0, 0, 0, 0,
                      0, 0, 1, 0, 1, 0, 0, 0, 0, 0,
                      0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
                      0, 0, 1, 0, 0, 0, 0, 0, 1, 0,
                      0, 0, 0, 0, 0, 0, 0, 0, 1, 0,
                      0, 0, 0, 0, 1, 0, 0, 0, 0, 0,
                      1, 0, 1, 0, 0, 0, 0, 0, 1, 0,
                      0, 0, 0, 0, 0, 0, 0, 0, 1, 0,
                      0, 0, 0, 0, 1, 0, 0, 0, 0, 0,
                      1, 0, 1, 0, 0, 0, 0, 0, 1, 0,
                      0, 0, 0, 0, 1, 0, 0, 0, 1, 0,
                      1, 0, 0, 0, 0, 0, 0, 0, 0, 0,
                      0, 0, 1, 0, 0, 0, 0, 0, 0, 0,
                      0, 0, 1, 0, 1, 0, 0, 0, 1, 0,
                      0, 0, 0, 0, 1, 0, 0, 0, 0, 0,
                      1, 0, 1, 0, 0, 0, 0, 0, 0, 0,
                      0, 0, 0, 0, 1, 0, 0, 0, 1, 0,
                      0, 0, 0, 0, 1, 0, 0, 0, 0, 0,
                      0, 0, 1, 0, 0, 0, 0, 0, 0, 0,
                      0, 0, 1, 0, 0, 0, 0, 0, 0, 0,
                      1, 0, 0, 0, 0, 0, 0, 0, 0, 0,
                      1, 0, 0, 0, 0, 0, 0, 0, 1, 0,
                      0, 0, 0, 0, 1, 0, 0, 0, 0, 0,
                      1, 0, 0, 0, 1, 0, 0, 0, 0, 0,
                      0, 0, 1, 0, 0, 0, 0, 0, 1, 0,
                      0, 0, 1, 0, 0, 0, 0, 0, 0, 0,
                      1, 0, 0, 0, 1, 0, 0, 0, 0, 0,
                      0, 0, 0, 0, 0, 0, 0, 0, 1, 0,
                      0, 0, 0, 0, 0, 0, 0, 0, 1, 0,
                      0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
                      1, 0, 1, 0, 0, 0, 0, 0, 0, 0,
                      0, 0, 1, 0, 1, 0, 0, 0, 1, 0,
                      1, 0, 0, 0, 0, 0, 0, 0, 0, 0,
                      1, 0, 0, 0, 0, 0, 0, 0, 0, 0,
                      0, 0, 0, 0, 1, 0, 0, 0, 1, 0,
                      1, 0, 0, 0, 1, 0, 0, 0, 0, 0,
                      0, 0, 0, 0, 0, 0, 0, 0, 1, 0,
                      0, 0, 1, 0, 1, 0, 0, 0, 1, 0,
                      0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
                      0, 0, 0, 0, 0, 0, 0, 0, 1, 0,
                      0, 0, 1, 0, 0, 0, 0, 0, 0, 0,
                      1, 0, 0, 0, 0, 0, 0, 0, 0, 0,
                      1, 0, 0, 0, 0, 0, 0, 0, 1, 0,
                      0, 0, 1, 0, 0, 0, 0, 0, 1, 0,
                      0, 0, 0, 0, 1, 0, 0, 0, 0, 0,
                      0, 0, 0, 0, 0, 0, 0, 0, 1, 0,
                      0, 0, 1, 0, 0, 0, 0, 0, 1, 0,
                      0, 0, 0, 0, 1, 0, 0, 0, 0, 0,
                      0, 0, 1, 0, 0, 0, 0, 0, 1, 0,
                      0, 0, 0, 0, 0, 0, 0};
int l, r;

signed main() {
    cin >> l >> r;
    int flag = 1;
    int cnt = 0;
    for (int i = 0; i < 168; i++) {
        if (prime[i] < l) continue;
        for (int j = i + 1; j < 168; j++) {
            for (int k = j + 1; k < 168; k++) {
                if (prime[k] > r) break;
                int a = prime[i];
                int b = prime[j];
                int c = prime[k];
                if (isprime[a * b % c] == 1 && isprime[a * c % b] == 1 && isprime[c * b % a] == 1) {
                    cnt++;
                    flag = 0;
//                    printf("{%d %d %d}",a,b,c);
                }
            }
        }
    }
    if (flag == 1) cnt = -1;
    cout << cnt;
    return 0;
}
























